The present invention relates to control systems for material handling vehicles and, more particularly, to software configurable distributed control network systems for material handling vehicles.
In order to improve the performance and handling characteristics of vehicles, including material handling vehicles, it is desirable to provide an onboard system which modifies the performance of vehicle components in response to external conditions. For example, it may be desirable to vary the maximum turning angle of the vehicle steer wheel inversely with respect to the vehicle speed. Further, systems have been developed to provide sensing and operator display of such conditions as battery discharge, traction motor brush wear and the need for scheduled maintenance.
An example of such a system is disclosed in Avitan et al. U.S. Pat. No. 4,942,529. That patent discloses a lift truck having a control system which includes a microprocessor that receives logic signals corresponding to such parameters as the inclination of the associated lift truck, and "end-of-aisle" location and angle of steering wheel orientation. The microprocessor also provides digital output signals to control such components as traction motor contactors. The system disclosed in the Avitan et al. patent is design to enter a "learn mode" during which a technician or operator is instructed, through a series of commands appearing on the display panel of the lift truck, to provide certain inputs to the microprocessor, such as placing the vehicle in a straight ahead steered wheel value, and placing the travel-controller in the full forward position.
The truck type is communicated to the microprocessor by setting an array of DIP switches to correspond to a particular vehicle type. The learn mode disclosed in the Avitan et al. patent is designed ostensibly to compensate for variations in response of system components, both initially and over time. However, there is no mechanism in the Avitan et al. patent for modifying the application program driving the microprocessor. Further, there is no readily available mechanism for modifying the learn program or the boot program inherent in the microprocessor of Avitan et al.
Further, it is known to provide a material handling vehicle with a microcontroller or module which includes a microprocessor and read only memory (ROM) that contains a complete library of application software for an entire fleet of vehicles. The microprocessor and the controller determines which set of application software to load into random access memory (RAM) by reading an identification tag which is physically associated with the lift truck. Such a system is disclosed in Kellogg et al. U.S. Pat. No. 5,113,344.
Accordingly, the controller mechanism of the Kellogg et al. patent is "universally" operative for every vehicle whose performance characteristics are contained in ROM. Again, however, in order to change the application software or modify the boot software of the microcontroller, it would be necessary to physically remove the ROM and replace it with ROM containing new instructions, or by replacing a card containing the ROM chip in the microcontroller.
Accordingly, there is a need for a system for controlling material handling vehicle in which the components of the lift truck are controlled by modules whose application software can be reconfigured without physical change of components. Further, there is a need for a material handling vehicle control system in which boot software and diagnostics can be conducted without modification of physical components.